The present invention relates to an impactor having grinding face arranged underneath the impact aprons at the side of the housing opposite to the feed material inlet, the grinding face extending at least partially under the rotor. Because of the close proximity of the grinding face to the rotor, which makes impossible the examination/replacement of its crushing implements in the operating position, the grinding face has been arranged so that it can be moved into a position away from the rotor. To do this, the grinding face of a known impactor described in German Patent DE-PS 19 34 545 has been arranged on a track, on which it can be retracted from the housing along with a section of the housing rear wall. Also, it has been tiltably arranged on a track in the known impactor described in German Published Patent Application DE-OS 30 30 913, so that it can be moved into a more or less horizontal position outside the housing, to facilitate replacement of worn parts, for example. Such designs require rails extending well beyond the impactor housing for the retraction of the grinding face, as well as correspondingly large adjusting cylinders and floor space.
In the case of another known impactor of the type described in German Patent DE-PS 25 16 014, the impact aprons and the grinding face are mounted on the outwardly swingable rear wall of the housing by axles provided at their lower ends and the grinding face is connected to the rear wall so that, when the rear wall swings outwards, the grinding face moves away from the rotor, executing a pivoting motion into a flatter position. The upper part of the grinding face is pivotably connected to the hinged rear wall of the housing, Whereas the lower part is connected via a linking means to the static section of the housing. When the rear wall swings outwards, the grinding face moves away from the rotor with an inclined upward motion, at the same time executing a slight outward movement, so that access to worn parts becomes easier for replacement purposes. However, in the case of impactors with grinding faces which extend underneath the rotor to a greater extent, this arrangement cannot be employed, since the bottom of the grinding path could enter the circle described by the rotor tips when the housing rear wall is opened.